Stencil printing machines of the type mentioned above are as such already known which provide an adjustment arrangement for material gripping and displacement arrangements, usually designated as gripper beams. This adjustment arrangement is intended to impart a precise position to the gripper beams in relation to a printing table in the printing machine. The gripper beams include members for gripping and displacing a material. For their movement the gripper beams interact with at least one, preferably two, endless feed chains or the like, which are arranged in parallel. These cease to move when the gripper beams are located in predetermined positions, one for the gripper beam to grip a sheet or material intended for printing, and one for the gripper beam to hold or leave a sheet in a position for application of print to the sheet. The gripper beams can be made adjustable by means of a double lever arm system so that the gripper beams adopt precisely the said predetermined positions, by providing the end surfaces of the gripper beams and the outer ends of a double lever arm system with interacting members.
Here the members comprise on the one hand convex, preferably cylindrical or spherical surfaces and secondly preferably "V"-shaped recesses which are intended to be pressed against each other in the predetermined position.
An adjustment arrangement of the type mentioned above has been described previously in British patent specification No. 1,208,614.
It is already known that the drive for the gripper beams described above with endless drive chains arranged in parallel becomes extremely complicated, because it is not only a question of driving the chains intermittently so that the gripper beams stop in predetermined positions, but furthermore tensioning arrangements are required for the chains and also other mechanical members. Furthermore it is known that a drive arrangement for gripper beams of the type mentioned above has to be dimensioned for high power input, because the construction as a whole becomes heavy and the acceleration and retardation moments require high power inputs.
There has long been a desire to be able to create conditions such that the drive arrangement for the gripper beams is made simple, while at the same time the gripper beam design is made light and simple, thereby making it possible to displace the gripper beams rapidly between two predetermined positions without excessive consumption of power.
Furthermore it is a difficult technical problem to create conditions such that the transport speed of the gripper beams is easily capable of regulation, for example so that the gripper beam is subjected to high acceleration, high velocity and a somewhat reduced retardation.
Furthermore there has been a desire, and this represents a difficult technical problem, to create conditions such that in connection with stencil printing machines, the material provided with a printed image can be delivered easily. It is particularly advantageous if special delivery belts and special delivery fingers can be eliminated.
A particular problem which has been encountered with stencil printing machines, especially with such stencil printing machines that function at high printing speeds, is that the insertion time for material intended to be printed to reach the insertion position is short and this becomes particularly difficult when insertion is carried out manually.